As semiconductor device feature sizes have decreased to sizes smaller than the wavelength of light used in photolithographic processes, the diffraction of light at feature pattern edges formed on the reticle causes a loss of resolution in transferring the reticle pattern to the wafer photoresist. To increase the resolution of photolithographic pattern transfer, phase shift masks have been developed where the phase of the wavefronts of light passing through alternating portions of the reticle pattern are shifted out of phase with respect to light passing through adjacent portions to produce destructively interfering wavefronts to reduce undesired exposure of the wafer photoresist due to diffraction of light at feature edges of the reticle pattern. As a result, the contrast, and therefore transferable resolution of the reticle pattern is improved.